The present invention relates to optical fiber alignment mechanism and connectors using it.
Optical fibers have been widely known as suitable means for transmitting optical signals in optical communication. In optical fiber communication systems, however, the loss of optical energy has always been a subject of discussion. When light is transmitted through optical fibers, there is caused not only transmission loss due to the fiber characteristics but also connecting loss due to the fiber interconnection. This invention aims at elimination of the latter loss. In order to eliminate or minimize such connecting loss, fiber alignment has to be achieved with accuracy of micron order, and at the same time, one fiber end has to closely abut the other opposite fiber end. Further, optical fibers are usually thin lines having a diameter of 100 microns order, so that fibers themselves are fragile and their ends can be moreso. Accordingly, fiber ends have to be provided with the structure that is suitable for protecting and reinforcing them. In order to attain fine fiber alignment mechanisms there have been a lot of trials. However, they have not always been successful in providing an entire solution to the problem. In the most popular structure that has been proposed thus far, the fiber end is molded by using a plastic resin. This is simple and effective to some extent. As is known, however, when the melting plastic resin stiffens, it never fails to shrink. Therefore, any fine adjustment of fiber alignment before plastic molding is in vain due to such shrinkage. Accordingly, it is not possible to achieve fine fiber alignment readily and reliably by such a simple molding method as mentioned above.
Another example of the prior art will be seen in the U.S. Pat. No. 4,087,155 which discloses a connector for a single optical fiber. For the optical fiber alignment, the prior art connector utilizes a tricuspid interstice formed by three spheres with equal diameter. The end of the fiber is mounted in that interstice. The spheres are further mounted in an elongated cylinder member. This arrangement will result in good fiber mating with high accuracy, because the tricuspid interstice formed by 3 spheres is smartly utilized to mount the fiber therein. Three spheres are contained in the cylinder member and then, two of said cylinder members are inserted into a single sleeve for coupling. In such a structure, however, the fiber alignment would become impossible if two cylinder members should be deformed by some cause. In other words, when an off-center state occurs between the inner and outer diameters of the cylinder member, the center of the fiber inserted into the sleeve becomes off-axis relative to the sleeve center, thus also producing another off-axis state against the fiber coming from the opposite side of said cylinder member. In order to solve such an off-center problem as mentioned above, it is necessary to form said cylinder member with extremely high accuracy, thus resulting in expensive connectors.
Still another prior art connector will be seen in the article entitled "Dual three-rod Connector For Single Fiber Optics" by B. D. Metcalf et al, which is carried by Applied Optics Vol. 18, No. 3, page 400-401, issued on Feb. 1, 1979. In the connector disclosed therein, there are used two sets of rods. One set comprises 3 rods having identical diameters and the other also comprises 3 rods having an identical diameter but smaller than that of the former set.
In this prior art connector, there are used two groups of rigid rods, the first one of which consists of three rigid rods having an identical diameter while the second one consists of a plurality of rods having an identical but larger diameter than the rods of the first group. In the first rod group, said three rods are arranged to have a tricuspid interstice therebetween formed thereby, into which an optical fiber is inserted and held. A part of the resultant structure by the arrangement above is then further inserted into an insert ferrule of predetermined length and secured therein to form a plug, where said three rods work as insert rods. On one hand, a plurality of said larger diameter rods are arranged, for example, to form a hexagonal cross sectional pattern by using seven rods, and then fixed by binding them altogether by means of O-rings. The pattern creates six interstices therein, and each of them is used as a receptacle for the insert rods of said plug. In other words, the fiber alignment has to be made eventually within the interstice formed by the larger diameter rods. As a result, the fiber alignment comes to be dominated by the interstice state which depends on the compression mode of said O-ring or the like. Further, the head of said insert rods are not fixed together, thereby making it harder to insert said insert rods into said interstices. Still further, tangential contact between the rods in the interstice is easily broken by external force abnormally added thereto. Still further, when some twisting force is applied thereto, the fiber location in the insert rods is easily changed thereby.